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1 Journal of the Korean Electrochemical Society Vol. 12, No. 3, 2009, J$M,$Mš ü6$m (E$M»yw»Á Á Á ³ w yw ( : k) Electrochemical Behavior of UCl 3 and GdCl 3 in LiCl-KCl Molten Salt Seul Ki Min, Sang-Eun Bae, Yong Joon Park, and Kyuseok Song Nuclear Chemistry Research Division, Korea Atomic Energy Research Institute, Daeduk daero 1045, Yuseong-gu, Daejeon , Republic of Korea (Received July 24, 2009 : Accepted July 29, 2009) š ywœ w»yw» š LiCl-KCl œ UCl 3ù GdCl U Gd»yw 3+ w. U š LiCl- KCl ü 0.2 V/ 0.35 V 4+ U y/y, 1.51 V/ 1.35 V /w vj 3+ ùkü. Gd 2.15 V vj, 1.9 V yw vj ùkü. U Gd yw š 3+ Gd vjƒ w. û w w ü y ew. r ƒq w»yw p r š w w vj ƒ û. Abstract : Electrochemical behaviors of U 3+ and Gd 3+ were investigated in LiCl-KCl eutectic molten salt by using various electrochemical techniques. The electrodeposition and dissolution currents for uranium show the maximum at 1.51 V and 1.35 V, respectively while, for gadolinium, at 2.15 V and 1.9 V, respectively. In case of LiCl-KCl molten salt containing both of U 3+ and Gd 3+, the peak potential of electrodeposition of gadolinium shifts to more positive potential than in the solution without U 3+. The potentials in chronopotentiometric data suddenly dropped to negative value as soon as the reduction currents were applied and became constant at the potential around which the U 3+ and Gd 3+ are electrodeposited. The results of normal pulse voltammetry (NPV) and square wave voltammetry show that those methods can be used to qualitatively analyze the elements in the melts. Especially, the differentiation of NPV result was found to be useful for the separation of the peaks of which potentials are close each other. Keywords : Pyrochemical processing, Uranium, Gadolinium, Electrochemical sensor, LiCl-KCl * sebae@kaeri.re.kr (SEB) and sks@kaeri.re.kr (SK) 276

2 1. 21» y š ùy w yk y ƒ s. p ƒ ù ù 1) ƒ ù ƒ» w v öš. ƒ yk jš» j ñš. ù x 40% wš 2030 ¾ 60%¾» w x ƒ. 2) zw s» sww», ƒw w x. x ù wy z š. w» (Advanced Fuel Cycle) œ» w, œ»yw» w œ š ywœ (Pyrochemical Processing). š yw œ zw z, LiCl-KCl œ 500 C š w» o yw w,, (electrochemical deposition)w z w. 2,3) š ywœ w» y w» w w»ywz, 12«, 3 y, š ü,, k» yw p v ƒ w. p zw w k p s wwš» w w y w x»yw p w l yw w. w š ywœ œ» w 4-10) š ü ƒ w v. w w k p Ÿ xÿ w Ÿw,»yw y w»yw ¾ y w,»yw ƒ ƒ w z ùkû ), š ywœ» w» p zw ƒ k ƒ w»yw p w. 2. x Fig. 1 š»yw d l. ƒ l y p (LiCl)/ ye (KCl) œ (anhydrous beads) gadolinium chloride (GdCl 3 ) Aldrich ( 9.999%) w. y (AgCl) Alfa Aesar t ( %) w š, UCl 3 Fig. 1. Schematic of the electrochemical measurement system in molten salt media.

3 278 J. Korean Electrochem. Soc., Vol. 12, No. 3, 2009 ü š BiCl 3 w w w w. 14) U+Bi 3+ U 3+ +Bi x w ù w ƒƒ l l w.» w. x, t s ü z Áò.» 1.0 mol% AgCl w w LiCl-KCl œ, 3 mm q š z (Ag) Ö Ag Ag» + w. 15) 2.3.»» e x Gamry Instruments Reference 600 potentiostat/galvanostat PC w w. ü d w K type Chromel-Alumel (themocouple) w. LiCl-KCl œ ƒ x 450 C 1 o w ³ w w. 3. š Fig. 2a UCl 3 LiCl-KCl œ l l w d w y š (cyclic voltammetry) ùküš. vj C 1 Fig. 2. Cyclic voltammograms obtained from W in LiCl- KCl melt containing mol/cm 3 UCl 3 (a) and mol/cm 3 GdCl 3 (b) at 450 o C. Scan rate was 200 mv/s. 3ƒ y y A V vj ùküš. vj 14) C 2 A 2 w yy ¾ w ƒ. wù (underpotential deposition) w» w 16) U(III) y U(I) yw x w Langmuir x w. w CV w w 17) Au(111) t 34 ù j w ùkþ, yy vj ƒ 10, k t w w ùkù (k š 18)) U(I) x k w. vj A 3 C 3 3ƒ 4ƒ yy v j 150 mv ƒ (quasi reversible) w. vj 14) Bi a Bi c UCl 3 w» w. 19) Fig. 2b GdCl 3ƒ ƒ LiCl-KCl š ü l l w d w y š. š 2.1 V y ƒ w 2.13 V vj ƒ ùkùš. w 2.1 V y ƒ» w 1.95 V vj ƒ ùk ù. 20) w, š ywœ p, ƒ k y. ü q w š y wœ, z w w.» x p, k ƒ k, yw, œ ùkù»yw y w. Fig. 3 UCl 3 GdCl 3 LiCl-KCl š œ l l w d w z» š (linear sweep voltammetry; LSV) ùküš. Fig. 2 ùkù, 1.4 V 1.5 V 3ƒ y v jƒ ùkù. w ƒ y y ƒ Fig. 2(b) w 1.99 V 1.85 V, vj ƒ 2.14 V 2.02 V w w. ƒ y, Fig. 2(b) t ù» ù -ƒ w» w. w 9)ù Al-Eu Al-U w 10)

4 w»ywz, 12«, 3 y, Fig. 3. Linear sweep voltammogram obtained from W in LiCl-KCl melt containing mol/cm 3 UCl 3 and mol/cm 3 GdCl 3 at 450 o C. Scan rate was 200 mv/s. w š Al-Eu w. Eu LiCl-KCl œ ù» LiCl-KCl œ ww. k w» w w ù w ƒw ww Al 4 Eu k w ü ù» Eu w. Al 4 Eu w, Eu w û. 9) w ƒ w w» w vjƒ w vjƒ ù kû w, x XRDù XPS w w ww š š nšw mw šw. Fig. 4 UCl 3 GdCl 3 LiCl-KCl š œ l l w d w (chronopotentiometry) š. š» (OCP) 0.3 V w ƒ ƒw wš ma/cm 2 ( ) ƒw» Fig. 2a vj C 2 w w 1.3 V ùkü ƒ 1.45 V y. w ƒw 39.5 ma/cm ma/ cm 2 (q ) ƒw ƒ. ƒw ƒ ƒw w ƒ ƒ y Fig. 4. Chronopotentiometric results obtained from W in LiCl-KCl melt containing mol/cm 3 UCl 3 and mol/cm 3 GdCl 3 at 450 o C. Fig. 5. Normal pulse voltammogram and its differentiated graph obtained from W in LiCl-KCl melt containing mol/cm 3 UCl 3 and mol/cm 3 GdCl 3 at 450 o C. de = 4 mv, T p = 0.2 s, and T m =1s. ü ƒš. d ü w. Fig. 5 Fig. 4 y r (normal pulse voltammetry; NPV) ww š. ƒ û ƒ ƒ ù yƒ y y w. w š w vj ƒ y ùkùš V y» w vjƒ, š 1.95 V 2.15 V j vjƒ ùkùš. Fig. 3

5 280 J. Korean Electrochem. Soc., Vol. 12, No. 3, 2009 Fig. 6. Square wave voltammogram obtained from W in LiCl-KCl melt containing mol/cm 3 UCl 3 and mol/cm 3 GdCl 3 at 450 o C. F = 10 Hz and de = 4 mv. r ƒ y vj e vjƒ w., LSV w NPV w vjƒ w ùkû. NPV w d ƒ k (steady-state) d». Fig. 6 Fig. 3 y ƒq (square wave voltammetry; SWV) ww š. Fig. 2 vjƒ w ƒ vj S/N ƒ Fig. 2 w j ƒ. w Fig. 5 NPV š ƒ y vj y. l, š ywœ»yw w, UCl 3 GdCl 3 š LiCl-KCl œ w»yw l pw. CVù LSV vjƒ š úe w SWVù NPV ƒ txwš. w w ƒw w ü ùkû. p k w»yw l w w»yw y»yw d š ywœ v w»yw» y. 5. š ywœ v w š ü w, p UCl 3, k GdCl 3 kw š LiCl-KCl UCl 3 GdCl 3»yw 3+ w. U š LiCl- KCl ü 0.2 V/ 0.35 V y/y, 1.51 V/ V /w vj ùk þ. Gd 2.15 V vj, 1.9 V yw vj ùkþ. U Gd yw š 3+ Gd vjƒ w t w ù U-Gd w» w. û w w ü y ew. ƒw ƒw ùkù w, y, ƒ y, ƒw. r ƒ q w» yw p r š w, w vj ƒ û. w š ywœ»yw». w» ww»,. š x 1. P. N. Pearson and M. R. Palmer, 'Atmospheric carbon dioxide concentrations over the past 60 million years' Nature, 406, 695 (2000). 2. D. K. Cho, S. K. Yoon, H. J. Choi, J. Choi, and W. I. Ko, 'Reference Spent Nuclear Fuel for Prprocessing Facility Design' J. Kore. Rad. Waste Soc., 6, 225 (2008). 3.J. H. Yoo, B. J. Lee, H. S. Lee, and E. H. Kim, 'Investigation of Pyroprocessing Concept and Its Applicability as an Alternative Technology for Conventional Fuel Cycle' J. Kore. Rad. Waste Soc., 5, 283 (2007). 4. O. Shirai, M. Iizuka, T. Iwai, Y. Suzuki, and Y. Arai, 'Electrode reaction of plutonium at liquid cadmium in LiC-KCl eutectic melts' J. Electroanal. Chem., 490, (2000). 5. T. Nagai, A. Uehara, T. Fujii, O. Shirai, N. Sato, and H. Yamana, 'Redox equilibrium of U 4+ /U 3+ in molten NaCl- 2CsCl by UV-Vis spectrophotometry and cyclic voltammetry' J. Nucl. Sci. Technol., 42, (2005). 6. Y. D. Yan, M. L. Zhang, Y. Xue, W. Han, D. X. Cao, and L. Y. He, 'Electrochemical study of the codeposition of Mg-Li-Al alloys from LiCl-KCl-MgCl 2 -AlCl 3 melts' J.

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